This invention relates to an electronic copying machine, more specifically to an improvement of a recording sheet separating device for de-electrifying a recording sheet separated from a photosensitive member after a toner image formed on a surface of the photosensitive member is transferred to the recording sheet.
Copying machines or other like apparatus generally use a device for separating a recording sheet from a photosensitive member to fix the recording sheet after a toner image on the photosensitive member is transferred to the recording sheet. With use of the separating device, the recording sheet bearing the transferred toner image thereon is separated from a photosensitive drum, and is wound around an insulating turn roller to shift its direction toward a fixing device. However, the recording sheet separated from the photosensitive drum, bearing electric charges, will suffer local discharge caused by a potential difference produced when it touches or approaches a carrier guide or other conductive material. If such local discharge is caused before fixation, toner on the recording sheet will be scattered to disturb the resultant toner image. In order to prevent the local discharge from affecting the recording sheet during the conveyance, therefore, a recording sheet 13 is conventionally de-electrified by means of a conductive brush 11 facing a photosensitive drum 10 before it is separated from the drum 10 by a separating claw 12, and then wound around a turn roller 14, or de-electrified by means of a conductive brush 17 disposed in a sheet passage 16, as shown in FIG. 1. Before the separation, however, the space for the setting of the conductive brush 11 is so narrow that the conductive brush 11 may often have its tip caught by the turn roller 14 to be damaged, or is liable to be contaminated by the scattered toner and will fail to sustain the de-electrifying effect. In the sheet passage 16, on the other hand, the recording sheet will bend as indicated by a broken line to vary the gap between itself and the conductive brush 17, so that it is difficult to adjust the location of the conductive brush 17, resulting in impossibility of stable de-electrification.
As an example of such a separating device, there is a device stated in Japanese Utility Model Disclosure No. 53-46843; Y. Aguro et al., Apr. 20, 1978. This device is so constructed that a conductive needlelike electrode with flexibility is brought into contact with a de-electrifying device from under a recording material at an inclination of 25.degree. to 45.degree. toward the discharge direction of a transfer material. In such a prior art device, however, de-electrification is performed on the fixing roller side without avoiding the aforementioned drawbacks.
In a device stated in Japanese Patent Disclosure No. 52-125331; K. Nakahata et al., Oct. 21, 1977, which is equivalent to the prior art device as shown in FIG. 1 hereof, de-electrification is performed after a recording material is separated from a photosensitive drum without obviating the aforementioned drawbacks.